Melatonin Administration Methods for Research in Mammals and Birds

Abstract

Endocrine research in animals often entails exogenous hormone administration. Special issues arise when developing administration protocols for hormones with circadian and seasonal periodicity. This article reviews various methods for the exogenous administration of hormones with such periodicities by focusing on melatonin. We discuss that methodological variations across studies can affect experimental results. Melatonin administration techniques used in vertebrates includes infusion pumps, beeswax pellets, oral administration, injections, SILASTIC capsules, osmotic pumps, transdermal delivery, beads, and sponges.

Effects of Duodenal 5-Hydroxytryptophan Perfusion on Melatonin Synthesis in GI Tract of Sheep

“…For example, it improves the meat quality and quantity of cashmere goats [ 13 , 14 ], reduces somatic cell count and mastitis in dairy cattle to improve the quality of the milk [ 15 , 16 ]. Currently, in husbandry industrial, the methods used to regulation of MT levels in animals are primarily to alter the light/dark cycle of the environments [ 17 , 18 ], or by implantation [ 19 , 20 ], injection [ 21 ], and oral administration [ 22 ] of MT. As to the exogenous melatonin administration, several factors should be considered including its bioavailability, acting duration, economic benefit, and delivery methods [ 22 ].…”

“…Currently, in husbandry industrial, the methods used to regulation of MT levels in animals are primarily to alter the light/dark cycle of the environments [ 17 , 18 ], or by implantation [ 19 , 20 ], injection [ 21 ], and oral administration [ 22 ] of MT. As to the exogenous melatonin administration, several factors should be considered including its bioavailability, acting duration, economic benefit, and delivery methods [ 22 ]. Additionally, exogenous MT supplementation seems to reduce endogenous MT synthesis and to down-regulate expression of the MT receptors [ 23 , 24 , 25 ].…”

Biocompatible polymeric microparticles serve as novel and reliable vehicles for exogenous hormone manipulations in passerines

“…Some techniques for exogenous hormone manipulations (e.g., silastic tubes) allow a continuous release of a target hormone for extended time (up to 4 weeks) (Fusani et al 2005; Ovid, Hayes & Bentley 2018), but in this study, we have only achieved an increase of systemic IGF-1 levels for a period of at least 7, but less than 16 days. However, non-biodegradable pellets or silicone tubes require surgery to replace the vehicle after depletion (Ovid, Hayes & Bentley 2018), and biocompatible polymeric microparticles require only an additional subcutaneous injection to achieve a prolonged release. When wild animals cannot be easily recaptured, adjusting the properties of the PLGA microparticles (e.g., size or resomer type) may offer a possibility to modify the release kinetics and achieve even longer-lasting hormone treatments (Sun et al 2008; Busatto et al 2018; Matejkova & Podhorec 2019; Patel, Jha & Patel 2021).…”

“…Capture, restrain, sampling, the application of anesthesia, and the hormone manipulation itself might cause distress and have negative consequences on individuals living in natural conditions and consequently lead to a potential decrease in fitness and/or survival (Putman 1995; Fusani et al 2005; Goutte et al 2010; Spée et al 2011; Bonier & Cox 2020; Huber et al 2021). In addition, the impact of the application process itself and the effects of the hormone treatment (e.g., induced physiological responses, behavioural changes) might depend on the condition and life-history stage of an individual, both factors that are difficult to control for in field conditions (Colwell et al 1988; Putman 1995; Criscuolo 2001; Ovid, Hayes & Bentley 2018). Finally, and contrary to many experiments in a clinical or preclinical setting, studies focusing on an ecological context of a given physiological response often aim to mimic hormone levels that correspond to a specific physiological phenotype within a population.…”

“…Hence, as Fusani (2008) reviewed, many pioneering studies on field endocrinology have been conducted on passerine species, and there are now a variety of safe options available to steadily release exogenous hormones over a specified timeframe (Beck et al 2016). They have been tested sufficiently on passerine species in the field and the laboratory (Fusani 2008; Müller et al 2009; Quispe et al 2015; Ovid, Hayes & Bentley 2018; Vitousek et al 2018).…”